Echo usually occurs in voice communications. After a signal to the receiving side is played by a receiver (also referred to as a headphone, an SPK or an earphone, etc.), crosstalk of this signal into a received signal of the transmitting side (also referred to as a microphone or a sound pickup, etc.) is realized through lines and acoustic reflection, and then this signal is fed to a far-end, so that a far-end correspondence contact person hears the echo. Echo will bring about great interference to both parties of a call, thereby influencing the quality of the call. In the event of large echo, it is also possible to cause the squeaking of the receiver and thus damage the receiver. In order to guarantee the quality of a call and the security of equipment, it is necessary to suppress echo in the voice communication.
From the generation mechanism, echo may be classified into two types, i.e., a linear echo component and a nonlinear echo component, wherein the linear echo component is generated by amplification and acoustic transmission of electroacoustic circuits, while the nonlinear echo component is generated by nonlinear distortion and acoustic transmission of a receiver. A self-adaptive echo elimination technology is usually employed for elimination of the linear echo component. Widely applied and mature, this technology may eliminate the linear echo component without damaging near-end voice. However, the elimination of the nonlinear echo component is likely to damage the near-end voice, thereby degrading the duplex performance, or even making channels be half-duplex.
The half-duplex phenomenon is very common in miniature hands-free voice communication equipment, because the receiver of such equipment, for example, a mobile phone or speakerphone having a hands-free function, has large nonlinear distortion and nonlinear echo component. With the increasing requirements on the fluency and conform level of voice communication, it is required to protect near-end voice and ensure duplex effect while suppressing echo. As the duplex loss mainly occurs during the elimination of the nonlinear echo component, it is particularly required to improve the nonlinear echo component elimination technology.
For the echo elimination of miniature hands-free voice communication equipment, one method for enhancing the duplex performance is to combine echo filtering and array space filtering with the help of a transmitter array, and then realize echo extraction and voice separation by signal difference of echo transmitted to each transmitter. For example, in the method as disclosed in Chinese Patent Application No. 201110326010.0, an approximately full-duplex call may be realized by array signal processing and echo elimination. However, this method needs to accurately judge the direction of arrival of echo and near-end voice to the transmitter array, so the consistency of transmitters is highly required. Not only the sensitivity of the transmitters needs to be consistent, the consistency of phase is much more required, so a strictly acoustic design is needed. However, in miniature hands-free equipment, due to compact structure and limited size, it is difficult to meet the requirements of the acoustic design, particularly of phase consistency. Therefore the application of this method is limited.